स ईड 54 (10574) WC र त य म नक IS 9417 क व व दत य प न क षण क मस द - प रबमलत क ट स चन क मलए उच च शव तत इस प त क सर य क मलए ल ड क न क मसफ र श

Transcription

1 व य पक पर च लन मस द हम स दर भ : स ईड 54 /ट अगस त 2016 तकन क सममतत : क क र ट प रबलन व षय सममतत,स ईड प र प तकत भ: मह दय, 1. मसव ल इ ज तनय व र ग पर षद क र चच खन ल सदस य 2. स ईड 54 क सर सदस य 3. र चच खन ल अन य तनक य न म ल ख त मस द स ग ह : क पय इस मस द क अव क कर और अप सम मनतय यह बत त ह ए भ ज कक यदद यह मस द प रक ल त ह त इस पर अम कर म आपक व यवस य अथव क र ब र म क य कद इय आ सकत ह सम मततय र जन क अ ततम ततच :30 मसत ब 2016 सम मनत यदद क ई ह त क पय अध हस त क षर क उपरल ख त पत पर य न म ल ख त ईम पर स ग फ म ट म भ ज address: sdrane@bis.gov.in and /or ced54@bis.gov.in यदद क ई सम मनत प र प त ह ह त ह अथव सम मनत म क व भ ष स ब ध त र दट ह ई त उपर क त प र क यथ वत अ नतम र प द ददय ज एग यदद सम मनत तक क प रक नत क ह ई त ववषय सलमनत क अध यक ष क पर म श स अथव उ क इच छ पर आग क क यशव ह क ल ए ववषय सलमनत क भ ज ज क ब द प र क अ नतम र प द ददय ज एग धन यव द प रल ख स ख य श षभक स ईड 54 (10574) WC र त य म नक IS 9417 क व व दत य प न क षण क मस द - प रबमलत क ट स चन क मलए उच च शव तत इस प त क सर य क मलए ल ड क न क मसफ र श यह प र भ रत य म क ब य र क व बस इट पर भ उप ब ध ह भवद य स लग न : उप मलखखत ( ब क लसन ह ) प रम (लसवव इ ज न यर ) ईम : ced@bis.org.in

2 DRAFT IN WIDE CIRCULATION ADVICE DOCUMENT DESPATCH Reference Date CED 54/T TECHNICAL COMMITTEE: CONCRETE REINFORCEMENT SECTIONAL COMMITTEE, CED 54 ADDRESSED TO: 1. All Interested Members of Civil Engineering Division Council, CEDC 2. All Members of CED All others interested Dear Sir (s), Please find enclosed the following draft: Doc. No. Title CED 54 (10574) WC DRAFT INDIAN STANDARD ()- RECOMMENDATIONS FOR WELDING OF HIGH STRENGTH STEEL BARS FOR REINFORCED CONCRETE CONSTRUCTION Kindly examine the draft revision and forward your views stating any difficulties which you are likely to experience in your business or profession, if this is finally adopted as National Standard. Last Date for comments: 30 September 2016 Comments if any may please be made in the format as given overleaf and mailed to the undersigned at the above address or on address: and/or In case no comments are received or comments received are of editorial nature, you will kindly permit us to presume your approval for the above documents as finalized. However, in case comments of technical in nature are received, then it may be finalized either in consultation with the Chairman, Sectional Committee or referred to the Sectional Committee for further necessary action if so desired by the Chairman, Sectional Committee. This document is also hosted on BIS website Thanking you, Yours faithfully, Encl: as above (B K Sinha) Head (Civil Engg.) ced@bis.org.in

3 FORMAT FOR SENDING COMMENTS ON BIS DOCUMENTS CED54 (10574 )-WC (Please use A4 size sheet of paper only and type within fields indicated. Comments on each clause/ sub clause/ table/ fig etc. be started on a fresh box. Information in column 3 should include reasons for the comments and suggestions for modified working of the clauses when the existing text is found not acceptable. Adherence to this format facilitates Secretariat s work) {Please your comments to ced54@bis.gov.in or sdrane@bis.gov.in or fax to } DOC. NO. & TITLE: Doc : CED 54(10574) WC- DRAFT INDIAN STANDARD (Second Revision of IS 9417) RECOMMENDATIONS FOR WELDING OF HIGH STRENGTH STEEL BARS FOR REINFORCED CONCRETE CONSTRUCTION LAST DATE OF COMMENTS: 30 September 2016 NAME OF THE COMMENTATOR/ORGANIZATION: Sl. No. Clause/Sub-clause/Para No. Comments/suggestions (1) (2) (3)

4 For BIS Use Only BUREAU OF INDIAN STANDARDS DRAFT FOR COMMENTS ONLY (Not to be reproduced without the permission of BIS or used as standard) Concrete Reinforcement Systems Sectional Last Date of Comments Committee CED Draft Indian Standard RECOMMENDATIONS FOR WELDING OF HIGH STRENGTH STEEL BARS FOR REINFORCED CONCRETE CONSTRUCTION () र त य म नक प रबमलत क ट स चन क मलए उच च शव तत इस प त क सर य क मलए ल ड क न क मसफ र श (IS 9417 क व व दत य प न क षण) ICS : BIS 2016 B U R E A U O F I N D I A N S T A N D A R D S MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI Month/Year Price Group XX

5 FOREWORD Formal clause will be added at later stage. This standard was first published in 1977 deriving assistance from DIN 4099 (Part 1):1972 Welding of reinforced steel Requirement and Tests issued by the Deutsches Institute for Normung and keeing in view the practices prevailing in the country at that time. In first revision in 1989, resistance but welding of cold worked bars has been deleted and reference to gas pressure welding of cold worked bars has been made. Also provision for the welding of cold worked steel bars conforming to grades Fe 415 & Fe 500 of IS In this revision of Indian standard major changes covered are considering the welding of online quenched steel bars for reinforced concrete construction which also includes high corrosion resistance (HCR) variety. These changes have been incorporated in light of the findings of a study conducted by WRI Trichy on the weldability of Cu-Cr and Cu-Thermomechanically Treated (TMT) bars/ online quenched steel bars for reinforced concrete construction. A new annexure (Annexure D) on Gas metal arc welding (GMAW) using CO2 is also been added. 1. SCOPE 1.1. This standard lays down recommendations for welding bars conforming to grades Fe 415, Fe 415D, Fe500 and Fe500D of IS 1786 High strength deformed steel bars and wires for concrete reinforcements-specifications(fourth revision) by flash butt welding, shielded metal arc welding, gas pressure welding and Gas metal arc welding (GMAW) using CO2 2. REFERENCES 2.1 The Indian Standards listed in Annexure A are necessary adjuncts to this standard. 3. TERMINOLOGY 3.1 For the purpose of this standard, definitions given in IS 812 shall apply. 4. PLANS AND DRAWING 4.1 Plans and drawing for welding reinforced bars shall be prepared in accordance with SP 46 : SYMBOLS 5.1 Symbols for welding used in plans and shop drawings shall conform to IS WELDING EQUIPMENT AND ACCESSORIES

6 6.1 Welding equipment and accessories used in welding of steel bars for concrete reinforcement shall conform to the requirements of the appropriate Indian Standards where available. Where an Indian Standard is not available, equipment and accessories shall be of the best available quality. Their capacity shall be adequate for the welding procedure. A general guidance for selection of equipment and accessories is included in Annex B. 7. PARENT METAL 7.1 The parent metal shall be of guaranteed wieldable quality of steel conforming to IS SAFETY AND HEALTH REQUIREMENTS 8.1 Safety and health requirements as prescribed in IS 818 shall be applicable. Fire precautions shall be as given in IS ELECTRODES 9.1 Electrodes used shall conform to IS WELDING PROCESSES AND PROCEDURES Online quenched bars shall be either butt welded or lap welded. Butt welding may be carried out either by flash butt, gas pressure or by shielded metal arc welding process. Lap welding may be carried out by shielded metal arc welding process and Gas metal arc welding (GMAW) using CO Bars of unequal diameter may be welded. However, in case of butt welding, the difference in diameter of bars shall not exceed 5 mm. Where unequal diameter bars are welded, the dimension d mentioned in this standard refers to diameter of the smaller bar The surface of the ends of the bars to be welded shall be clean and free from rust, paint, grease and/or other contaminants which are likely to affect the quality of weld Flash Butt Welding of Online Quenched Steel Bars Flash butt welding may be adopted if a large number of welding has to be done at the same place and when the electric supply is available of the required capacity in respect of the cross sectional area of the maximum size of the bar to be welded Procedure The ends of the bars to be welded should be placed in proper alignment in clamps so that bent or eccentric joints do not result. The clamps should be cleaned before each welding operation to avoid current loss and to eliminate harmful notches or grooves due to burning in of spots of arcing.

7 The bar ends shall be uniformly pushed against each other from the moment of contact to the up-setting. The transformer regulator should be so set that the current at the contact area is between 85 to 90 A/mm If the capacity of butt welding machine or the available power is not sufficient to take the load for welding from cold, welding may be done after preheating. By making and breaking of the contact arc repeatedly, heat can be made to spread over the entire cross section of the bar. He number of short-circuits (contacts and reversing) should be kept to the minimum possible so that the welding time and spread of heat in the longitudinal direction in the bar is minimum. Satisfactory joints with only slight reduction in original strength of the bar can be achieved with current density up to 25 A/mm In automatic machines, the flash rate should be so set that a continuous flash without interruption can be achieved. If the rate is set, too high additional short-circuits are required leading to heat spread. If the rate is too low, the flash will be interrupted and consequently air penetrating into the joints will form oxides. If the machine is handoperated, the flash should be maintained to avoid interruption For bars with sheared ends, a burn-off (flash-off) length of about 5 to 7 mm is required (this length is practically independent of the bar diameter). Very short burn-off lengths lead to defective welding because all the impurities may not have been removed from the place of welding. Increase in the burn-off length will spread heat along the length of the bar thus reducing the strength of the bar The up-setting should result from the burning off, that is, without interruption in the rain of sparks. The electric supply should be switched off about 1/3 to 1 second after the start of the up-setting or in the case of automatic machine after 1 to 3 mm of up-set travel. The voltage and frequency of the current should be checked before commencing the welding operation. Deviations from the nominal value or large fluctuations during the operation may lead to gross defects in welding. Wherever possible, welding should be done during day time when the total load on the network is fairly balanced Butt-Welding by Shielded Metal Arc Welding Process General Butt-welds by metal arc welding process are normally adopted to join bars of thickness more than 20 mm Preparation for Welding The preparation of the edges of the rods shall be as shown in Fig.1. The edges shall be prepared by shearing, machining, or oxy-acetylene flame cutting. Beveling may

8 be made by machining, grinding oxy-acetylene cutting. The fusion faces and the surrounding material shall be free from scale, dirt, greases, paint, Rust and contaminants When it is not possible to rotate the bars for carrying out all welding in flat position, the edge preparation shall be such that welding is done on both sides in the vertical position All the bars to be butt welded should be aligned and set up in position with their axis in one straight line. This may be done in a jig or by means of a clamp or by using guides. Rotation of the bars should be avoided until they are adequately welded so that no disturbance to the alignment is caused and no twist is introduced in the bars during the process of welding. The joints may not be out of alignment by more that 25 percent of the thickness of the thinner material for material up to and including 12 mm thick, or by more than 3 mm for thicker material Electrode Welding electrodes with flux covering of Type 3 or Type 6 of IS 814 are recommended for better results depending on the size of the bar to be welded. Storage of the latter type and their drying immediately prior to use must be strictly in accordance with the recommendation of the electrode manufacturer The size of electrodes depends upon the position of the bead and thickness of the bar to be welded. The root runs should be made with electrodes of size not exceeding 2.5 mm. For successive beads, the size of the electrodes should be progressively increased so that in the top bead, the electrode size does not generally exceed 3.15 mm for 20 mm bars and 5 mm for 40 mm bars Concentration of heat shall be avoided by proper welding sequence and manipulation of electrodes.

9 Procedure The sequence of welding beads is shown in Fig.2. The runs 1 to 4 are made in the position of welding best suited for the quality of the weld. Besides the interruption in welding required for cleaning of each bead, a pause shall be made after every second bead and the bar is allowed to cool. The temperature of the bars at a distance of about one bar diameter from the joints shall not exceed 300 o C immediately after the bead is made. Before commencing the next bead, the temperature shall not exceed 250 o C. The temperature may be checked approximately by using temperature indicating crayons. However, in the absence of temperature indicating devices, the bar may be allowed to cool down to hand hot temperature before the next bead is deposited. After completing bead 4, the bars are turned through 180 o and the beads 5 to 7 are made in the same manner as described above. The top bead 8 is deposited as the joint is continuously rotated and the size of the reinforcement should be approximately as indicated in Fig In the case of non-rotatable bars, the beads 1 to 4 should be made as explained in The welder then moves to the other side and beads 5 to 7 are similarly made. It is difficult to deposit a uniform top bead for non-rotatable bars and it may be necessary to make two or more separate annular runs so that the joint is approximately axisymmetric and has sufficient reinforcement as shown in Fig Butt Welding by Gas Pressure Welding Process Gas pressure welding is basically a hot forging process of joining the two bars end to end. The bar ends are heated by a multi-nozzle burner using oxy-acetylene flame and fused by forcing the two bar ends against each other under pressure to effect a solid phase welded joint.

10 10.5 Lap Welding of Online Quenched Steel Bars General Lap joints may be made in online quenched steel bars of all sizes. They are preferred when access for welding is from one side only, and while connecting prefabricated units. Use of electrodes with flux covering of Type 3 or Type 6 of IS 814 are recommended for better results depending on the size of bar being welded. Storage of the latter type and their drying immediately prior to use must be strictly in accordance with the recommendations of the electrode manufacturer Preparation for Welding Edge preparation is not necessary for lap welds. The joint faces and the surrounding material shall be free from scale, dirt, grease, paint, rust and contaminants Electrodes The size of electrodes according to the diameter of the bar to be welded shall be as follows: Normal Diameter of Bar, d Size of Electrode, Max mm Up to and including Over 10 up to and including Over 18 up to and including Over Procedure The arc should be struck as shown in Fig.3. Somewhere in the middle of the joint and not at its beginning. The movement of the electrode for welding lap joints in the horizontal and vertical position is indicated in Fig.3. The various lap joints used to connect cold-worked bars are shown in Fig.4 to 7. In Fig. 4 to 6, the dimensions indicated as 5d for single side welding should be halved to 2.5d if the welds are deposited from the opposite side also. The single-strap arrangement shown in Fig.7 is not recommended where access is from one side only. In the case of joints illustrated in Fig.6 and 7, the strap material must also conform to 7 and the strap cross sectional area must, at least, equal that of the bar to be joined Gas Metal Arc Welding (GMAW) may be employed using CO2

11 GMAW uses a continuous and consumable wire electrode and CO2 as the shielding gas. This welding procedure should be carried out indoors. GMAW is not recommended for butt joints Annexure D gives more information about GMAW 11 VISUAL INSPECTION 11.1 Shape of Profile The profile of the welds shall be uniform, slightly convex and free from overlap at the toes of the welds.

12 11.2 Uniformity of surface CED54 (10574 )-WC The weld surface shall be uniform in appearance throughout its length and shall show no pronounced hump or crater Degree of undercut The welded joint shall be free from undercut but slight intermittent occurrences may be disregarded Freedom from Surface Defects The surface of the weld shall be free from cracks, cavities, solid inclusions and other visible defects Misalignment The misalignment of the bars welded shall not exceed one-fourth of bar diameter or 5 mm whichever is less. 12 INITIAL TESTS 12.1 Prior to production welding, test welds shall be carried out under the local production conditions to establish that the proposed joints can be made satisfactorily. For the purpose, the tests shall be the same as for Quality Control Tests in 13 but only 3 test pieces will be required for tensile test and 3 for bend test. Such initial tests shall be repeated if there is any change in: a) the welding process; b) the grade of online quenched steel bars; c) the type or size of electrode; d) the welder; and e) the position of welding, unless the new position is an easier one. 13 Butt Welds 13.1 Butt Welds Test pieces containing butt welds at the centre in the as-welded condition shall be selected at the rate of one for tensile test and one for bend test for every 100 joints or as decided by the engineer-in-charge Tensile Test

13 Unmachined specimens with a free length bet- ween grips about 20d should he used. The selected pieces when subjected to a tensile test shall have tensile strength not less than 90 percent or the actual tensile strength of the bar but in no case less than 485 MPa for grade Fe 415 and 545 MPa for grade Fe 500 of IS The fracture shall not take place in the weld joint Bend Test The welding flash or reinforcement shall be removed at the point where contact is made with the mandrel. The welded joint shall be capable of being bent to an angle of 60 o around a mandrel of diameter specified below, before any crack appears: Nominal Diameter of Bar, d Diameter of mandrel mm mm Up to 10 5 d Over 10 7 d 13.2 Lap Joints Test pieces containing lap joints at their centre in the as-welded condition shall be selected at the rate of one sample for tensile test for every 100 joints or as decided by the engineer-in-charge Tensile Test The free specimen length between grips must be between 25 d and 30 d where d is the nominal diameter of the bar. The breaking load shall not be less than the guaranteed load in accordance with IS 1786 required to fracture the bar. 14 RETESTS 14.1 If a sample selected for testing fails to meet the requirements given under 13.1 and 13.2, the purchaser or his representative shall take two further samples from the same lot. If on testing, either of the samples fails to meet the specified requirements, the whole lot shall be rejected.

14 ANNEX A (Clause 2.1) CED54 (10574 )-WC LIST OF REFERRED INDIAN STANDARDS Is No. SP 46: 2003 IS 812:1957 IS 813: 1986 IS 814: 2004 IS 818:1968 IS 1179:1967 IS 1786: 2008 IS 1851: 1997 Title Engineering drawing practice for schools and colleges Glossary of terms relating to welding and cutting of metals Scheme of symbols for welding (first revision) Covered electrodes for manual metal arc welding of carbon and carbon manganese steel-specification (sixth revision) Code of practice for safety and health requirements in electric and gas welding and cutting operations (first revision ) Specification for equipment for eye and face protection during welding (first revision) High strength deformed steel bars and wires for concrete reinforcements specification (fourth revision) Single operator type arc welding transformers- specification (third revision ) IS 2635: 1997 DC electric welding generators-specifications ( third revision ) IS 2641: 1989 IS 2751: 1979 IS 3016:1982 IS 9595: 1996 IS 9857: 1990 Electric welding accessories-specifications (first revision) Code of practice for welding of mild steel plain and deformed bars for reinforced construction ( first revision) Code of practice for fire precautions in welding and cutting operations Metal arc welding of carbon and carbon manganese steels- Recommendations (first revision) Welding cables- specifications (first revision)

15 ANNEX B (Clause 6.1) CED54 (10574 )-WC SELECTION OF EQUIPMENT AND ACCESSORIES FOR WELDING COLD-WORKED BARS USED FOR REINFORCED CONCRETE CONSTRUCTION B-1 GENERAL z B-1.1 The methods of welding covered in this annex are: a) Flash butt welding, and b) Shielded metal arc welding with covered electrodes. B-2 FLASH BUTT WELDING EQUIPMENT B-2.1 The efficiency of the flash butt welding equipment, manifested by its conjunctive efficiency for cold-worked steels should be about 8 kva/cm of the cross sectional are2 of the bar in order that sufficient cold weld may be accomplished. B-2.2 The jaws for clamping the bars should preferably be long and pin shaped in order to assume 2 rectilinear central feeding of the bar ends. The joint should preferably be of copper to assume a smooth and uniform flow of current from the jaws into the bar. B-3 SHIELDED METAL ARC WELDING EQUIPMENT B-3.1 In its simplest form, the equipment required for shielded metal arc welding of coldworked steel bars for concrete reinforcing consists of: a) Welding power source; b) Accessories, such as, electrode holders, earth clamp, welding cable, connectors, chipping hammer and wire brush; c) Protective equipment for the operator, such as, hand screen or helmet, gloves, apron, etc; and d) Suitable electrode storage and drying equipment, where necessary. B Welding Power Source The current for welding may be alternating or direct. There is little to choose between them for work involving mild steel welding. Electricity from the mains is usually at too high a voltage for are welding. Various types of equipment are used for reducing this voltage and delivering a welding current of right characteristics. B Alternating current transformer of oil-cooled or air-cooled type has the advantage of being low in initial cost and requiring very little maintenance. Various types of controls for varying the current to suit conditions are in common use. Some of these are: (a) a static choke with tappings, (b) a choke the value of which may be varied by means of the movement of the core, (c) a choke with a saturable core, and (d) a variable

16 flux linkage transformer. Being essentially a single-phase load, welding transformers when connected to 3-phase supply mains may cause slightly unbalanced load conditions. Condensers of adequate rating may also be connected across the input lines for improving the power factor. B Rotary machines, such as, motor generators suitable for use on alternatingcurrent mains give a direct current output of the required characteristics. They have the advantage- that they impose a balanced load on 3-phase supply mains. They are, however, initially more expensive and require more maintenance than transformers. B Where the mains supply is direct current, a motor generator designed for direct current mains use has to be selected. B Rectifier welding sets which are relatively high in initial cost, require very little maintenance because of elimination of most moving parts. They also impose a balanced load on 3-phase supply mains. B For work at sites where mains power supply is not available, a petrol or diesel engine driven welding generator may be selected. Such machines are often mounted on trailers for easy portability. B Other points to be considered when selecting the equipment are: a) that the machine is designed to work satisfactorily in the climatic conditions that will be met with during service; b) that it is well made and conforms to relevant Indian Standards, wherever these exist; and c) that the current capacity is adequate for welding with the sizes of electrodes expected to be used. B IS 1851 covers transformer welding equipment and IS 2635 covers motor generator equipment for manual metal arc welding. B Electrode holders shall conform to the requirements laid down in IS 2641 and shall be of suitable rating for welding with electrodes in sizes expected to be used. B Welding cables shall conform to the requirements laid down in IS 9857, if cables with copper conductors are used. Cables with aluminium conductors shall be of a quality proved for performance. Two lengths of cables are required, one from the welding set to the electrode holder and the other from the work piece to the welding set. B All cable terminal connections, such as, sockets-earth clamp, shall also conform to the requirements specified in IS 2641.

17 B A well-made chipping hammer with a hardened and tough cutting edge and a narrow type wire brush which may reach the root of the weld would also be required for deslagging and cleaning the weld. B Protective Equipment A non-conducting hand screen or helmet fitted with protective filter lens will be required to protect the face and eyes of the operator from the ultra-violet and infra-red rays emitted by the arc. The filter lens has the double function of securing good vision of the arc and giving effective protection by cutting off the harmful rays. The eye and face protection equipment should conform to the appropriate stipulations laid down in IS B Aprons and leather gloves should be of a standard that has been proved adequate for welder s use. Shoulder guards, leggings and other such protective garments may be necessary when the operator has to do positional welding in conditions where freedom of movement is restricted. B Storage The conditions of the electrodes used have an important bearing on the ultimate quality of the weld produced. Particularly, when moist ambient conditions are envisaged, for instance, at site work, the storage of electrodes has to be given much attention. Heated storage cabinets or drying ovens arc a must when low hydrogen type electrodes are being used for site work. Other types of electrodes also are preferably stored before use in such cabinets when ambient conditions are unfavourable. ANNEX C (Clause ) GAS PRESSURE WELDING C-1 GAS PRESSURE WELDING PROCESS The gas pressure welding process may be used for butt welding of reinforcing bars. C-1.1 Preparation for Welding C The ends of bars and the extreme un- twisted ends of new bars shall be cut by shearing or machining to make the face approximately normal to the axis of the bar. Care should be taken to ensure that the bar ends do not twist while shearing. C Rust, oil, paint, cement paste and any other coating over the bar-ends shall be removed and the surfaces to be welded shall be finished as flat as possible. C-1.2 Procedure C Bars are clamped securely in the clamping unit with no misalignment keeping the gap between the bar ends less than 3 mm.

18 C To begin with, the bar ends are heated by a reducing flame to avoid any oxide formation. The flame shall be directed at the joint and the burner shall be rotated to ensure uniform heating of the bar ends. On sufficient heating, the gap between the bars ends shall be closed by the application of axial pressure (preliminary or first stage pressurization). C After preliminary pressurization and complete closing of the gap, the bar ends shall be heated by a neutral flame. The heating shall be done for an appropriate period ensuring that the bar ends do not melt. C On sufficient heating of the bar ends, appropriate axial pressure (final or second stage pressurization) is applied so that the bulge at the weld interface is about 1 4 times the bar diameter. Heating shall be stopped at this stage. However, pressure application shall be maintained for some time even after the flame is put off. C The bars shall be unclamped after the glow of the heated area vanishes. C In case the flame dies out during heating, the affected area shall be cut off and the welding procedure begun afresh. C-2 GAS PRESSURE WELDING EQUIPMENT C-2.1 The equipment for gas pressure welding comprises of: a) Oxygen and acetylene gas cylinders with regulating values, etc; b) Multi-nozzle burner; c) Clamping unit; and d) Pressurizer. C The burner consists of a blow pipe with four or more nozzles. The nozzles shall be so arranged to ensure uniform heating of the bar surface. The burner shall provide stable flame during heating and the heating capacity shall be appropriate to the size of the bar. C The clamping unit shall grip the bars well, be easy to handle, capable of being used in horizontal or vertical position of welding, and have such mechanism that no misalignment develops at the welded portion. C Pressurizer shall be either hydraulic or mechanical and may be either manually operated or electrically driven. The pressurizer shall be capable of maintaining uniform axial pressure

19 ANNEX D (Clause ) CED54 (10574 )-WC GAS METAL ARC WELDING USING CO2 D-1 GAS METAL ARC WELDING PROCESS The Gas Metal Arc Welding Process using CO2 may be used for lap welding of online quenched steel bars. However, in view of the constraint of space for the torch, butt welding is not recommended. D-2 GAS METAL ARC WELDING EQUIPMENT D-2.1 The equipment for Gas Metal Arc Welding consists of: a. Welding gun and wire feed unit; b. Welding Power Supply; c. An electrode; and d. Shielding gas (CO2) supply. D The most common welding gun is a hand held air-cooled gun, it is used for general welding. The second most common type of welding torch is water-cooled, it uses higher current levels for heavier sections and larger wire diameters. The third typical holder type is an automatic gun that is water cooled; this gun is used typically with automated equipment. D Most applications of gas metal arc welding use a constant voltage power supply. As a result, any change in arc length (which is directly related to voltage) results in a large change in heat input and current. A shorter arc length will cause a much greater heat input, which will make the wire electrode melt more quickly and thereby restore the original arc length. This helps operators keep the arc length consistent even when manually welding with hand-held welding guns. To achieve a similar effect, sometimes a constant current power source is used in combination with an arc voltage-controlled wire feed unit. In this case, a change in arc length makes the wire feed rate adjust in order to maintain a relatively constant arc length. In rare circumstances, a constant current power source and a constant wire feed rate unit might be coupled, especially for the welding of metals with high thermal conductivities, such as aluminum. This grants the operator additional control over the heat input into the weld, but requires significant skill to perform successfully. Alternating current is rarely used with GMAW; instead, direct current is employed and the electrode is generally positively charged. Since the anode tends to have a greater heat

20 concentration, this results in faster melting of the feed wire, which increases weld penetration and welding speed. The polarity can be reversed only when special emissivecoated electrode wires are used, but since these are not popular, a negatively charged electrode is rarely employed. D Electrode selection is based primarily on the composition of the metal being welded, the process variation being used, joint design and the material surface conditions. Electrode selection greatly influences the mechanical properties of the weld and is a key factor of weld quality. In general the finished weld metal should have mechanical properties similar to those of the base material with no defects such as discontinuities, entrained contaminants or porosity within the weld. To achieve these goals a wide variety of electrodes exists. All commercially available electrodes contain deoxidizing metals such as silicon, manganese, titanium and aluminum in small percentages to help prevent oxygen porosity. Some contain denitriding metals such as titanium and zirconium to avoid nitrogen porosity. Depending on the process variation and base material being welded the diameters of the electrodes used in GMAW typically range from 0.7 to 2.4 mm ( in) but can be as large as 4 mm (0.16 in). The smallest electrodes, generally up to 1.14 mm (0.045 in) are associated with the shortcircuiting metal transfer process, while the most common spray-transfer process mode electrodes are usually at least 0.9 mm (0.035 in). D Shielding gases are necessary for gas metal arc welding to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. This problem is common to all arc welding processes; for example, in the older Shielded-Metal Arc Welding process (SMAW), the electrode is coated with a solid flux which evolves a protective cloud of carbon dioxide when melted by the arc. In GMAW, however, the electrode wire does not have a flux coating, and a separate shielding gas is employed to protect the weld. This eliminates slag, the hard residue from the flux that builds up after welding and must be chipped off to reveal the completed weld. Typical gas-flow amounts are approximately l/min (40 50 ft³/h).